1. Field of the Invention
The present invention relates to a laser diode emitting laser light in a lamination direction.
2. Description of the Related Art
A Vertical Cavity Surface Emitting Laser (VCSEL) consumes lower power than that of an edge emitting laser, and is able to be directly modulated. Thus, in recent years, the VCSEL has been used as an inexpensive optical communication light source.
The VCSEL is generally provided with a columnar mesa in which a lower DBR layer, a lower spacer layer, an active layer, an upper spacer layer, an upper DBR layer, and a contact layer are layered in this order on a substrate. In one of the lower DBR layer and the upper DBR layer, to improve efficiency of current injection into the active layer and lower the threshold current, a current narrowing layer having a structure that a current injection region is narrowed is provided. Electrodes are respectively provided on the top face of the mesa and the rear face of the substrate. In the laser diode, a current injected from the electrode is narrowed by the current narrowing layer, and then injected into the active layer, and thereby light is emitted due to electron-hole recombination. The light is reflected by the lower DBR layer and the upper DBR layer, laser oscillation is generated in a given wavelength, and the light is emitted as laser light from the top face of the mesa.
In recent years, a GaN VCSEL using a sapphire substrate or a GaN substrate as a substrate has been developed (for example, Y. Higuchi, K. Omae, H. Matsumura, and T. Mukai, Applied Physics Express 121102, 2008; J. W. Scott, R. S. Geels, S. W. Corzine, and L. A. Coldren, Journal of Quantum Electronics, vol. 29, No. 5, 1295, 1993; and J. M. Elson, J. P. Rahm, and J. M. Bennett, Applied Optics, vol. 22, No. 20, 3207, 1983).